Presently available absorbent articles such as diapers, sanitary napkins, incontinence briefs, and the like are generally very good at absorbing aqueous fluids such as urine and blood. However, during typical use such articles become saturated at the impingement zone while other zones removed from the impingement zone will remain dry. As a result, a substantial portion of the total absorbent capabilities of such articles remains unused. Thus, it is desirable to have a means for transporting the aqueous fluids from the impingement zone to other areas of the absorbent article to more fully utilize the article's total absorbent capability.
Filaments capable of spontaneously transporting aqueous fluids such as water offer improved drainage over other types of filaments such as those disclosed in European Patent Application 0223908 and in U.S. Pat. No. 4,443,492. European Patent Application 0223908 discloses thermally bonded webs composed of polyester, polypropylene, or polyethylene hydrophobic fibers which are coated with acrylic acid partially neutralized by alkali metallic salts and crosslinked simultaneously with polymerization to form webs coated in situ with superabsorbant polymer. The webs have increased absorption of fluid when used in a sanitary product such as a diaper, but the individual fibers of the web do not possess the ability to transport fluid from the crotch area to lesser utilized areas of the absorbent core.
U.S. Pat No. 4,443,492 describes the coating of cellulose fiber based material with a water soluble monomer which is converted into a water-absorptive polymer. This type of material has poor absorption performance because the monomer is able to penetrate inside the fiber base material and fill the capillaries between filaments. The mode of wicking in this prior art is totally in the capillaries between the fibers. The diameter of the capillaries is reduced by the coating. As the coating swells in the wet state the capillaries are blocked off.
The present inventors have discovered that certain filaments having "U" and "E" shaped cross-sections with stabilizing legs more efficiently transport and drain aqueous fluids than filaments capable of spontaneously transporting fluids having other shapes. For example, various H-shaped filament cross-sections have been disclosed. U.S. Pat. No. 4,707,409 describes H-shaped filaments extruded through an orifice defined by two intersecting slots and each intersecting slot in turn defined by three quadrilateral sections connected in series. Copending commonly assigned U.S. patent application Ser. No. 07/736,267, filed Jul. 23, 1991, also discloses H-shaped filaments. The problem with such H-shaped filaments, however, is that the parallel wall channels with flat bottoms and small corner sections hold onto fluids and thus inhibit drainage.
U.S. Pat. No. 4,364,996 discloses U-shaped filament cross-sections with projections. The projections, however, do not stabilize the curved sections of the fiber. Moreover, the U-shaped fibers described in U.S. Pat. No. 4,364,996 do not have straight sections
In contrast, the present inventors have overcome such deficiencies with "U" and "E" shaped fibers with stabilizing legs. Such "U" shaped fibers have straight and curved sections but do not have small corner sections to hold on to fluids. Thus, the "U" shaped fibers of the present invention provide complete drainage. Such "E" shaped fibers provide a wider top area which allows for improved acquisition of fluids and additional channels which lead to increased vertical movement against gravity when compared to H-shaped fibers. The use of strategically placed stabilizing legs allow the fibers to maintain their shape.